Metal-plastic-metal laminates have been described in various U.S. and foreign patents. Exemplary patents include U.S. Pat. Nos. 3,582,427, 4,229,504, 4,204,022, 4,313,996, 4,369,222, 4,424,254 and EPA No. 19,835. These laminates are useful as light weight replacements for sheet steel in cars and trucks. Relatively thin laminates are useful in flexible packaging end use applications while relatively thick laminates are useful as construction laminates.
Methods of preparing such laminates are also known. One method includes bringing at least one layer of plastic and at least one layer of metal into intimate contact and subjecting them to suitable heat and pressure, using, for example, a platen press. A more efficient and continuous method involves the well known extrusion processes--extrusion coating or extrusion lamination. Often an intermediate layer of adhesive or primer, in the form of a film or coating, is used in conjunction with these methods to insure adequate adhesion between the metal substrate and plastic.
In the past, one primary incentive for considering the replacement of sheet steel with metal-polymer laminates was the weight saving that could be obtained with equivalent stiffness. Placing thin steel skins on the outside of the laminate makes optimal use of high yield, high modulus steel and allows the structurally ineffective (in bending) middle portion of the composite to be light weight plastic, resulting in the primary advantage of steel-plastic laminates--weight reduction versus an equivalent stiffness sheet steel, but at substantially less cost penalty compared to other weight-reducing materials such as aluminum sheet. In other cases it has been desired to obtain sound or vibration damping from the laminate.
One of the basic limitations of many of the prior art metal-polymer laminates is the lack of sufficient high-temperature stability to enable the laminate to pass through current automotive bake ovens. A satisfactory high temperature laminate must not exhibit significant distortion at 205.degree. C. Metal polymer laminates having cores of rigid engineering thermoplastics meet this requirement. Such metal-polymer laminates however tend to delaminate in conventional sheet metal forming processes due to the lack of ductility of the adhesion bond between polymer and metal. A new laminate has now been found that does possess adequate heat distortion characteristics and good ductility.